Specialized diodes as light-emitting devices have slowly been incorporated into more and more applications. In virtually every application, particularized technical issues have presented themselves, issues that arise both from starting with older designs and from the inherent characteristics of light-emitting diodes, or LEDs.
LEDs have several major benefits in comparison to non-LED lighting. If properly installed and treated, an LED has a longer life span than many comparable light elements. Thus, LEDs have been or work is being undertaken to devise manners to incorporate LEDs into applications where it is costly and/or difficult to replace the light elements. Relative to size, an LED can produce a greater amount of light, measured in lumens, than a comparatively sized non-LED light. For this reason, LEDs have been incorporated into many applications requiring small-sized light elements. Related to the greater light is the ability of LEDs to provide more light relative to power consumption than other lighting.
As an LED provides more light, the obvious corollary of greater light with respect to power consumption is that an LED wastes less power in the form of heat. While this is true, a large portion of generated heat is lost not on the light-emitting side of the diode, but instead at its base. The diode, which would be recognized as an electrical circuit component, is typically mounted on a printed wiring or printed circuit board, referred to herein as a PCB. The heat generated by the diode is initially transferred to the PCB, and the PCB is often heat-sinked in some manner. An 8-watt LED that has been properly installed and has proper heat dissipation may have a ten-year life span of daily 8-hour usage, while the same LED may fail in approximately twenty minutes without a heat sink.
Some efforts have been made to incorporate LEDs into pole or stanchion-type lights, such as what would typically viewed as an outdoor lamp or lantern and may be referred to as a streetlight. Traditional streetlights require bulb replacement and exhibit a heavy electrical cost burden for municipalities, shopping centers, retail establishments, and commercial zones, for example. In line with traditional approaches to construction, LED-based streetlights have an internal assembly that is mounted inside of an outer shell. The internal assembly is hardwired with the LEDs and, often times, each individual LED is separately mounted with the internal assembly. Beyond the labor required, each LED must be ensured of proper mounting so that the heat dissipation is proper, and the LEDs and connecting wires are susceptible to damage during handling and manufacture. Moreover, these designs are difficult or impossible to reconfigure or retrofit (such as altering the lighting elements) or replace/repair.
This internal assembly typically includes a main body formed of cast aluminum for the heat dissipation or heat sinking properties. The body often includes a top surface or area that includes fans to increase the surface area with the atmosphere. However, when the internal assembly is mounted within its outer shell, the fans are exposed to a cavity of air within the shell, and the air acts as an insulator. The result is that this type of prior art LED light has poor heat dissipation beyond the heat sink.
An LED is not unlike a traditional light-emitting element in that the element itself does little to control the direction of cast light. For many applications, and most outdoor applications, established patterns of cast light are usually specified. These patterns are often referred to by definitions provided by the Illuminating Engineering Society (IES). For instance, a Type III pattern is an oval or elliptical pattern wherein the light is cast in lateral directions from the lantern, while Type IV is similar to Type III, but the former casts the oval in a forward direction relative to the lateral directions. Both Type III and Type IV patterns may be specified for streetlighting in a residential area so that a lantern mounted proximate to but out of the roadway casts its light principally downward and into the street, and does not cast appreciable light towards the residences along the roadway. A Type V pattern is a generally symmetrical distribution.
In some applications, there is also a “cutoff” specification for determining how much light may be cast upwards from the lantern, demonstrating a concern for “light pollution” and light nuisance in urban areas. The IES defines a “full cutoff” as zero lumens at 90 degrees from vertical plumb or nadir. “Cutoff” requires 2.5% or less of total candlepower (i.e., measured lumens) at 90 degrees from nadir, while “semicutoff” requires 5% or less at 90 degrees from nadir.
The construction of the lantern itself creates issues for satisfying the pattern and cutoff specifications. In one prior art LED-based lantern, the LEDs are individually mounted in a ring around a circular internal assembly. The internal assembly includes a central support for positioning the ring to have the LEDs direct light downward in a generally circular pattern, and the central support includes a reflective surface formed on a concave cylinder. While the reflective surface serves to distribute light outward, the lower portion flares outwardly so that downward rays are reflected laterally, the concomitant result being that light is also reflected upwardly.
The principal manner used to control the throw or cast of light is reflective lenses. In a typical lantern, the outer shell includes a top portion or canopy, and light is emitted outward from the lantern below the canopy. In order to promote the low cutoff properties, the canopy also extends outwardly (horizontally) beyond any lens and is solid and opaque. A first style of lens is generally a translucent body or series of panels extending from the lower skirt of the canopy to a top of a lantern base, the base also being solid and opaque and providing structure support between the lantern and the stanchion upon which it is mounted. This style of lens may be clear, may be frosted, may have a pattern formed on the surface of the lens to reflect the light in a specific direction, or a combination of both. These lenses are heavy, and they can be expensive to manufacture and replace (such as when struck by vandals) or change (such as when the light Type pattern is to be changed).
Another style of lens is sometimes referred to as an “optic” or to as “optics.” This style utilizes a separate lens dedicated to a singular light-emitting element, though a plurality of lenses may be formed as a sheet. The individual lenses are placed close to the LEDs to generally capture most of the light from the LED and may be used to reduce the overall size requirements for the assembly.
A common drawback of the above-described prior art lanterns is the use of reflection to direct the light rays. As is know, reflection is the physical principal of a light ray hitting a reflective barrier, broadly treated herein as an internal or external surface or boundary for which a light ray strikes at an angle of incidence, the light then being turned away from the boundary at an angle of reflection. Reflection of light results in certain portion of the rays being lost to diffusion, for a variety of reasons. At a minimum, the lost rays are wasteful; at a maximum, they can be reflected at greater than 90 degrees to the nadir.
Accordingly, there has been a need for an improved light assembly and, in particular, an improved LED-based lantern assembly.